1. Field of the Invention
The present invention relates to optical lenses and light emitting diodes using optical lenses, and more particularly to a side-emitting light emitting diode typically employed in a direct type backlight module of a liquid crystal display.
2. Discussion of the Related Art
Typically, a light source of a backlight module is one of the following two types: a cold cathode fluorescence lamp (CCFL), or a light emitting diode (LED). Disadvantages of a CCFL include high energy consumption, low optical uniformity, and poor purity of white light. In addition, after being repeatedly used over time, a brightness of the CCFL becomes degraded and a color of light emitted by the CCFL tends to shift. In general, the service life of a CCFL is about 15,000 to 25,000 hours. Furthermore, a CCFL only covers 75 percent of color space as defined by the National Television Standards Committee (NTSC). Therefore, using a CCFL cannot satisfy the requirements for a high quality color liquid crystal display. Unlike CCFLs, high powered LEDs can cover as much as 105 percent of color space as defined by the NTSC. In addition, these LEDs have other advantages such as low energy consumption, long service life, and so on. Therefore, high power LEDs are better suited for producing high quality color liquid crystal displays. In particular, side-emitting high power LEDs are widely used in direct type backlight modules of such liquid crystal displays.
FIG. 6 illustrates a side-emitting LED 10 of relevance. The LED 10 includes a light output unit 11, and an optical lens 13 coupled to the light output unit 11. The optical lens 13 includes a light input surface 131, a top interface 133 opposite to the light input surface 131, and a peripheral light output surface 135 generally between the light input surface 131 and the top interface 133. The light output surface 135 includes a first refractive surface 1351, and a second refractive surface 1353 adjacent to the first refractive surface 1351. The first refractive surface 1351 has the shape of a periphery of a frustum. The second refractive surface 1353 has the shape of an outer portion of a flat-topped dome. The LED 10 further includes a reflective surface 15 covering the top interface 133. Light rays emitted by the light output unit 11 enter the optical lens 13 through the light input surface 131 and transmit to the top interface 133. Many or most of the light rays undergo total internal reflection at the top interface 133 or are reflected back into the optical lens 13 by the reflective surface 15, and then exit the optical lens 13 through the light output surface 135. The light output surface 135 is configured to refract and bend light so that the light rays exit from the optical lens 13 at angles as close to 90 degrees relative to a central axis 16 of the LED 10 as possible.
Typically, the optical lens 13 is manufactured by injection molding technology. However, the structure of the light output surface 135 is relatively complex. This means an injection mold used for making the optical lens 13 is correspondingly complex. Thus the cost of making (or purchasing) and maintaining the injection mold may be unduly high.
What is needed, therefore, is an optical lens and light emitting diode using the optical lens which can overcome the above-described shortcomings.